The present invention concerns apparatus providing a monitoring system for monitoring respiratory and/or abnormal movements of subjects and to a method for carrying out such monitoring. More particularly, the invention pertains to a non-contact monitoring system specifically adapted to monitor respiration and/or convulsive movements of infants, although the invention is not necessarily limited thereto. A "non-contact" system means that the apparatus need not be physically connected to the person of the subject.
Generally, electronic devices for monitoring movement are known. For example, burglar alarms which employ ultrasound, i.e., ultrasonic sound waves, reflected off a moving person to trigger an alarm have been described. These devices employ the Doppler shift of the reflected ultrasound to trigger the alarm circuit. Accordingly, such devices measure movement velocity of a person or object and are incapable of reliably measuring small periodic movement such as the respiratory displacement of the chest and abdomen of a person, particularly of an infant.
Monitors specifically designed to detect infant apnea are also known. For example, see the article "Infant Apnea Monitors" in Health Devices, November 1974, Pages 3-23. This article deals with a number of different apnea monitors. Generally, these monitors require the infant to lie upon a special pad or mattress, to have electrodes attached to the infant's body, or to detect air flow through the mouth and/or nose of the infant by a special mask attached to the infant.
An infant apnea monitor which employed the Doppler shift of reflected microwaves was at one time on the market. However, this instrument was apparently too sensitive to nonrespiratory motions and so was deemed unreliable and subsequently discontinued from use.
U.S. Pat. No. 3,875,929 discloses the use of microwave radar to detect respiratory movement of a subject's chest and abdomen.
The use of microwave to detect infant respiration patterns is discussed in an article "Non-Invasive Home Monitoring of Respiratory Patterns in Infants" by C. I. Franks, D. M. Johnston, and B. H. Brown in Develop. Med. Child Neurol., 1977, 19, pages 748-756.
The use of ultrasonic waves in diagnostic apparatus is well known in the art as is illustrated by U.S. Pat. Nos. 3,778,756; 3,830,223, 3,771,355; 3,744,479; 3,856,985; and 3,606,879. "Ultrasound Recording of Fetal Breathing" is the title of an article by H. B. Meire, P. J. Fish, and T. Wheeler in the British Journal of Radiology, 1975, 48, pages 477-480, disclosing the use of ultrasound for in utero monitoring.
U.S. Pat. No. 3,938,500 discloses the use of a piezoelectric crystal transducer positioned beneath an infant to detect any form of movement resulting from reaction to an auditory signal.
U.S. Pat. No. 3,993,995 discloses a respiration monitor based upon reflection of a sonic, optical or radio wave trained upon the subject and employing means to receive the reflected wave and to generate signals responsive to the phase difference between the reflected and transmitted waves to indicate respiration extrema.
While monitoring of respiration or other movements of a subject or patient is necessary or desirable in any number of situations, it is particularly important in connection with the care of premature and low birth-weight infants, and infants with low Apgar scores. Such infants frequently have problems with respiration, particularly in the first few days after birth. Cessation of breathing (apnea) can occur and if respiration does not resume in time, anoxia resulting in permanent damage and/or death follows. It is therefore obviously of extreme importance to reliably monitor respiration to detect apnea and sound an appropriate alarm. It is also important in many cases to detect excessive movement of a subject, such as convulsive or hyperrespiratory movement.
It is accordingly an object of the present invention to provide a novel apparatus to reliably and accurately monitor movement and lack of movement, including respiratory movement, of a subject and to sound an alarm when conditions warrant.
It is another object of the present invention to provide an apparatus for monitoring apnea in infants or other subjects, which does not require physical contact with the subject.
It is another object of the present invention to provide a novel apparatus providing a motion monitor which will respond to apnea and optionally to excessive or convulsive-type movements by sounding an appropriate alarm, and which will not sound a false-alarm caused by extraneous gross movements, such as the movement of persons attending the subject.
It is another object of the present invention to provide a novel method and apparatus for monitoring the degree of respiratory effort and, optionally, other movements of the subject by reflecting ultrasonic sound waves from the person of a subject to be monitored.
Other objects and advantages of the invention will become apparent from the following description thereof.